So far, there have been known various disposable body warmers, or so-called "chemical body warmers" of the kind wherein heat is generated by exotheric reaction of chemical compounds. The commercially available disposable body warmers generally comprise a heat generating composition comprising powder of an easily oxidizable metal such as iron and an oxidizing agent, which are packed in a bag. In use, the metal powder and oxidizing agent are mixed with each other to allow the metal powder to react with the oxidizing agent, thereby generating heat. In such body warmers, the heat generating composition is generally added with additives to control the heat-generating characteristics including life and maximum temperature.
However, the chemical body warmers of the prior art are generally designed for winter use, so that the temperature of the body warmers rises to 40.degree. C. and above at the lowest. Thus, if the body warmer is used for a long time as a hot compress for a patient in a hospital, there is a fear of thermal burn at a low temperature. In addition, because the transfer of heat from the chemical warmer depends on thermal conduction, the user can feel a warmth on his skin near the warmer, but cannot have a warmth to the bone.
On the other hand, with a recent widespread of air conditioning systems, there is an increasing harmful influence on the health of occupants who must work for a long time in air-conditioned spaces such as office buildings, automobiles, factory work areas and the like. Because preferences vary considerably from person to person, some persons are in need of body warmers even in summer. However, the chemical body warmers of the prior art cannot be used for this purpose since they are too hot to use in summer.